Deflectable interconnect

ABSTRACT

A package for connecting an integrated circuit to a printed circuit board. The package includes an interconnect having a deflectable cantilever and a solder bump. When the integrated circuit is affixed to the interconnect, the solder bump deflects the cantilever. When the solder bump is heated such that the solder reflows, the cantilever springs toward its non-deflected position and is at least partially absorbed by the reflowing solder.

RELATED APPLICATIONS

[0001] This present application is a divisional of U.S. application Ser.No. 09/929,616, filed on Aug. 14, 2001, entitled “DEFLECTABLEINTERCONNECT,” which is a divisional of U.S. application Ser. No.09/352,802, now U.S. Pat. No. 6,285,081, filed Jul. 13, 1999, entitled“DEFLECTABLE INTERCONNECT” The present application incorporates theforegoing disclosures herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates in general to integrated circuitpackages and more particularly to ball grid array (BGA) packages.

[0004] 2. Background

[0005] An increasing consideration in the design and use of integratedcircuits is the package in which the integrated circuit (IC) resides. AsICs become more complex, and printed circuit boards become more crowded,IC packages continually need more leads or pins while their footprintsconsume smaller and smaller areas. In an effort to meet these demands,developers created the ball grid array (BGA) package.

[0006] A typical BGA package includes an IC affixed to a flexiblepolymide tape. A very thin conductor or wire bond connects a pad on theIC to a conductive trace on the polymide tape. The conductive trace isrouted to a solder ball. The solder ball is one of an array of solderballs that connect to the opposite side of the polymide tape andprotrude from the bottom of the BGA package. These solder ballsinterconnect with an array of pads located on a substrate, such as aprinted circuit board. Accordingly, the typical BGA package electricallyconnects each pad on an IC to a pad on a printed circuit board.

[0007] Typical BGA packages have drawbacks arising from the differentcoefficients of thermal expansion for the IC and the polymide tape. Ingeneral, the coefficient of thermal expansion of a material correspondsto the degree in which the material will expand when heated and contractwhen cooled. As the IC and the polymide tape expand and contract atdifferent rates, the wire bond experiences stress and tension. Suchstress and tension may cause the wire bond to loosen or break, therebydisconnecting the IC from the printed circuit board.

[0008] To compensate for stress and tension caused by thermal expansion,designers have developed IC packages without wire bonds. Oneconventional package is a “flip chip” package. A flip chip packageincludes an IC affixed to a polymide tape with a thick adhesive suchthat the pads of the IC are positioned over a layer of conductivetraces. Gaps in the adhesive provide room for a plurality of solderbumps that are used to connect the pads of the IC to the conductivetraces. Similar to the typical BGA package, the conductive traces arerouted to downward facing solder balls, which connect with pads of asubstrate, such as a printed circuit board.

[0009] Accordingly, the solder bumps of the flip chip package provide anelectrical connection from the pads of the IC to the layer of conductivetraces. Unfortunately, several drawbacks of these packages can prevent agood electrical connection from happening. For example, the solder bumpand adhesive dimensions need to be matched with a great deal ofaccuracy. When the solder bump diameter is small as compared to thethickness of the adhesive, the solder bump cannot connect the pads ofthe IC to the conductive traces. On the other hand, when the solder bumpdiameter is large as compared to the thickness of the adhesive, then theadhesive layer cannot sufficiently affix the IC to the tape.Furthermore, when the solder bumps are heated to cause the solder toreflow, air pockets or bubbles can form. These air pockets not only makefor a poor electrical connection, but also further exacerbate therelatively narrow tolerances allowed for the solder bump and adhesive.

[0010] These drawbacks can cause the loss of an electrical connectionbetween the IC pads and the conductive traces. Such loss lowers yieldrates, which in turn increases the overall cost of package manufacture.

SUMMARY OF THE INVENTION

[0011] One aspect of the invention is to provide a package having anelectrical connection between an IC and an interposer. The packagecomprises a solder bump, a solder ball, and an interconnect having adeflectable cantilever. When the IC is affixed to the interconnect, thesolder bump applies surface tension to the deflectable cantilever,thereby causing the cantilever to deflect downward. When the solder bumpis heated and the solder reflows, the reflowing solder releases thesurface tension on the cantilever. According to one aspect of theinvention, the cantilever then springs back toward its originalposition, within the reflowing solder. Thus, the reflowing solderpartially absorbs the cantilever.

[0012] In one embodiment, use of a deflectable cantilever advantageouslyprovides for greater absorption of the interconnect into the solder,thereby reducing the possible effects of air pockets. In anotherembodiment, use of a larger diameter solder bump advantageously providesmore solder, thereby also reducing the possible effects of air pockets.

[0013] Another aspect of the invention relates to a ball grid arraypackage for an integrated circuit. The ball grid array packageinterconnects a plurality of solder bumps on an integrated circuit witha plurality of solder balls located on the exterior of the ball gridarray package. The ball grid array package comprises at least one solderbump attached to an integrated circuit and at least one solder ballwhich is configured to interface with a printed circuit board. The ballgrid array package further comprises an interposer with at least onepocket and at least one via, wherein the pocket is configured to receivethe solder bump and wherein the via is configured to receive the solderball.

[0014] The ball grid array package further comprises a conductiveinterconnect circuit which electrically interconnects the solder ball inthe via with the solder bump in the pocket. The conductive interconnectcircuit further comprises at least one deflectable cantilever whichextends into the pocket such that the deflectable cantilever ispartially absorbed by the solder bump in the pocket.

[0015] One embodiment of the invention relates to an integrated circuitpackage that comprises at least one solder connection attached to anintegrated circuit. The integrated circuit package further comprises asubstrate with an opening which is configured to receive the solderconnection attached to the integrated circuit. The integrated circuitpackage also comprises a resilient cantilever which extends into theopening such that the resilient cantilever applies pressure to thesolder connection during reflow.

[0016] Another embodiment of the invention relates to an apparatus thatcomprises an interconnect layer with a first opening. The apparatusfurther comprises a conductor layered above the interconnect layer. Theconductor comprising a deformable portion that extends into the firstopening, wherein the deformable portion has resiliency that urges thedeformable portion into a solder connection.

[0017] An additional embodiment relates to an integrated circuit packagethat comprises a first solder connection in communication with anintegrated circuit. The integrated circuit package further comprises aninterconnect layer having a first opening. The integrated circuitpackage also comprises a conductor layered above the interconnect layer.The conductor comprising a deflectable portion that extends into thefirst opening, wherein the deflectable portion has resiliency that urgesthe deflectable portion into the solder connection during reflow.

[0018] One embodiment of the invention relates to an apparatuscomprising a substrate with an opening. The apparatus further comprisinga conductive layer above the interconnect layer. The conductive layercomprising at least two malleable portions which extend into theopening. In another embodiment a package comprises an integrated circuithaving a pad and a solder connection in communication with the pad. Thepackage further comprises a partially deflected first conductor and apartially deflected second conductor. The partially deflected first andsecond conductors each at least partially absorbed by the solderconnection.

[0019] In an additional embodiment, an apparatus comprises a substratewith an opening. The apparatus further comprises a conductive layerabove the interconnect layer. The conductive layer comprising at leasttwo flaps which extend into the opening. Yet another embodiment relatesto a package that comprises an integrated circuit having a pad and asolder bump in communication with the pad. The package further comprisesa deflectable conductor having partially deflected multiple flaps. Thepartially deflected multiple flaps are at least partially absorbed bythe solder bump, wherein the absorption of the partially deflectedmultiple flaps is caused by the partially deflected multiple flapsmoving from a deflected position toward a non-deflected position whenthe solder bump reflows.

[0020] One embodiment of the invention relates to a package for anintegrated circuit that comprises an adhesive having a thickness and asolder bump having a diameter greater than the adhesive thickness. Thepackage further comprises a conductive trace having a deflectablecantilever, wherein the deflectable cantilever deflects into a pocketwhen the adhesive layer affixes the integrated circuit to the conductivetrace. The cantilever also springs toward its original position when thesolder bump reflows. The package also comprises a solder ball and a tapeattached between the conductive trace and the solder ball.

[0021] Another embodiment of the invention relates to a method forforming a package for an integrated circuit that comprises attaching asolder bump to an integrated circuit and forming a pocket in aninterposer. The method further comprises tracing an interconnect overthe interposer such that a deflectable portion of the interconnectextends over a portion of the pocket. The method also comprises affixingthe integrated circuit to the interposer such that the solder bumpdeflects the deflectable portion of the interconnect into the pocket.

[0022] An additional embodiment relates to a method for forming apackage for an integrated circuit. The method comprises heating a solderbump to at least partially melt the solder bump. The method furthercomprises allowing a deflectable portion of an interconnect to springtoward a non-deflected position of the deflectable portion. The methodalso comprises partially absorbing the deflectable portion into thesolder of the solder bump.

[0023] Yet another embodiment of the invention relates to a method forforming a package for an integrated circuit. The method comprisesforming an interconnect with at least two resilient conductors. Themethod further comprises deflecting the two resilient conductors withsolder and heating the solder to at least partially melt the solder. Themethod also comprises allowing the two resilient conductors to springinto at least a portion of the solder.

[0024] One embodiment of the invention relates to a method for forming apackage for an, integrated circuit. The method comprises forming aninterconnect with at least one deflectable flap and deflecting the flapwith solder. The method further comprises heating the solder to at leastpartially melt the solder and allowing the flap to be absorbed by atleast a portion of the solder bump.

[0025] Another embodiment of the invention relates to a method forforming an electrical connection between solder and a conductivematerial. The method comprises using solder to apply a surface tensionon a deflectable portion of a conductive material, thereby deflectingthe deflectable portion. The method further comprises heating the solderbeyond a melting point, thereby substantially reducing the surfacetension on the deflectable portion. The method also comprises partiallyabsorbing the deflectable portion into the solder as the deflectableportion springs back toward its approximate original position.

[0026] An additional embodiment of the invention relates to a method forforming an electrical connection between solder and a conductivematerial. The method comprises using solder to deflect a cantilever andheating the solder beyond a melting point. The method further comprisespartially absorbing the cantilever into the solder as the cantileversprings back toward a non-deflected position.

[0027] Yet another embodiment of the invention relates to a method forforming an electrical connection between solder and a conductivematerial. The method comprises using solder to deflect a cantilever froma first position to a second position and heating the solder beyond amelting point. The method further comprises at least partially absorbingthe cantilever into the solder such that the cantilever moves from asecond position to a third position.

[0028] One embodiment of the invention relates to a device thatcomprises means for affixing an integrated circuit to a conductivelayer. The device further comprises means for deflecting the conductivelayer and then partially absorbing the conductive layer, therebyelectrically connecting the integrated circuit to the conductive layer.

[0029] For, purposes of summarizing the invention, certain aspects,advantages and novel features of the invention have been describedherein above. Of course, it is to be understood that not necessarily allsuch advantages may be achieved in accordance with any particularembodiment of the invention. Thus, the invention may be embodied orcarried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein. Furthermore, Otheraspects and advantages of the invention will be apparent from thedetailed description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is described in more detail below inconnection with the attached drawings, which are meant to illustrate andnot to limit the invention, and in which:

[0031]FIG. 1A is an exploded view of an electrical device, in accordancewith one embodiment of the invention;

[0032]FIG. 1B is a cross-sectional view of the electrical device of FIG.1A;

[0033]FIG. 2 is a cross-sectional view of a package having a deflectablecantilever, prior to attachment of an IC, according to anotherembodiment;

[0034]FIG. 3 is a top view of the deflectable cantilever of FIG. 2;

[0035]FIG. 4 is a cross-sectional view of the package of FIG. 2, afterattachment of the IC;

[0036]FIG. 5 is a cross-sectional view of the package of FIG. 2, afterreflow of the solder bump;

[0037]FIG. 6 is a cross-sectional view of a package having dualdeflectable cantilevers, prior to attachment of an IC, according to yetanother embodiment;

[0038]FIG. 7 is a top view of the dual deflectable cantilevers of FIG.6;

[0039]FIG. 8 is a cross-sectional view of the package of FIG. 6, afterattachment of the IC;

[0040]FIG. 9 is a cross-sectional view of the package of FIG. 6, afterreflow of the solder bump; and

[0041]FIG. 10 is a top view of a multi-flap cantilever, according to yetanother embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0042] While illustrated in the context of forming an electricalconnection between an IC and an interposer, the skilled artisan willfind application for the deflectable cantilever disclosed herein in awide variety of contexts. For example, the disclosed deflectablecantilever has utility in providing an electrical connection when solderis used as a conductor, such as within a BGA package.

[0043]FIGS. 1A and 1B illustrate an electrical device 100, including apackage 105, and a substrate 110. FIG. 1A illustrates an exploded viewof the electrical device 100, while FIG. 1B illustrates a crosssectional view of the same. The electrical device 100 finds use in awide variety of applications. For example, the package 105 can be usedin any electronic circuit needing the attachment of an integratedcircuit or the die 115 to the substrate 110, such as the attachment of amicroprocessor to a printed circuit board.

[0044] In the illustrated embodiment of FIGS. 1A and 1B, the package 105comprises the die 115, pads 120, solder bumps 125, an adhesive 130, aninterposer 135 having interconnects 140, and solder balls 145. The die115 will be understood by one of ordinary skill in the art to be anyintegrated circuit. For example, the die 115 can be from a wide range ofintegrated circuit products, such as: microprocessors, co-processors,digital signal processors, graphics processors, microcontrollers, memorydevices, reprogrammable devices, programmable logic devices, and logicarrays. In one embodiment, the die 115 comprises a memory device.

[0045] The pads 120 are shown in broken lines to indicate that they areon the reverse side of the die 115. In one embodiment, the pads 120electrically connect the die 115 to a variety of other devices, signals,or other “off chip” systems. It will be understood by one of skill inthe art of semiconductor package design that throughout the disclosure,the number of pads 120, solder bumps 125, interposer 135, interconnects140, solder balls 145, etc. are illustrated for clarity with only a fewexamples. In reality, there may be many pads 120 on the die 115. Forexample, commercially available memory devices from Micron Technology,Inc. include a 60-pin DRAM and a 100-pin SRAM, having 60 and 100 pads,respectively.

[0046] The pads 120 are electrically connected to the solder bumps 125.Such connection can be by commercially available processes, such asthose offered by Flip Chip Tech. In one embodiment, the solder bumps 125are small approximate spheres of solder. However, it will be understoodthat a wide variety of shapes could be used. For example, the solderbumps 125 could be in the shape of a pin or a cylinder or be any type ofsolder connection.

[0047] As illustrated in FIG. 1B, the package 105 includes the adhesive130 for affixing the die 115 to the interposer 135 and the interconnects140. In one embodiment, the adhesive 130 includes a number of adhesivegaps or adhesive pockets 133, which make room for the solder bumps 125.The adhesive 130 should also be strong enough to properly affix the die115 to the interposer 135 and the interconnects 140, such that thesolder bumps 125 deflect a portion of the interconnects 140, asdiscussed in more detail below. In one embodiment, the adhesive 130comprises a thermal plastic polymer, however, it will be understood thatthe adhesive 130 can be a variety of products. For example, the adhesive130 can comprise any thermal set, thermal plastic, or any adhesive. Suchproducts are commercially available from various manufactures such as:Ablestik, Sumioxy, Dow Coming, and Hitachi.

[0048] As illustrated in FIG. 1A, the interconnects 140 are conductivepaths or traces from the physical locations of the solder bumps 125 tothe physical locations of the solder balls 145. In one embodiment, theinterconnects 140 are a resilient, yet malleable conductive materialsuch that they provide spring or memory as well as conductivity. Forexample, when a surface tension is placed on the interconnects 140, theyshould deflect in a direction corresponding to the surface tension. Whenthe surface tension is removed, the interconnects 140 “spring” back inthe direction of their original position. A wide variety of conductivematerials exhibit such properties. For example, in one embodiment, theinterconnects 140 include gold plated copper. However, it is understoodthat other conductive materials and combinations are also suitable, suchas, but not limited to, copper, gold, aluminum, and various alloys.

[0049] The interconnects 140 can also comprise a wide variety of tracepatterns, in a wide variety of sizes and layers. For example, theinterconnects 140 trace from the physical positions of the solder bumps125 to the physical positions of the solder balls 145 along a singlelayer. However, it is understood that multiple layers of theinterconnects 140 could trace through multiple layers of the interposer135 in order to provide sufficient physical space for the amount of theinterconnects 140 needed to correspond to the amount of pads 120 on thedie 115.

[0050] In one embodiment, the interposer 135 provides on one side asurface upon which the interconnects 140 are traced, and on the otherside a connecting point for the solder balls 145. In one embodiment, theinterposer 135 is a flexible “tape” substrate comprising insulatingmaterial, such as polymide tape. It is understood that other substratescould also be used, such as thermoplastic, thermoplast, epoxy, flexcircuits, printed circuit board materials, or fiber materials. Polymidetape and analogous materials are commercially available from Shinko,Sumitomo, Compass, 3M, Casio, Packard-Hughes, Hitachi Cable, Cicorel,Shindo, Mitsui MS, and Rite Flex.

[0051] Further, the interposer 135 includes the vias 150 for attachingthe solder balls 145 to the interconnects 140. In one embodiment, thevias 150 correspond. to a predefined pattern of the solder balls 145 forthe package 105. Using pre-defined patterns for the solder balls 145allows the output mechanisms, e.g., the solder balls 145, to remainconstant over changing patterns of the pads 120 corresponding tochanging the die 115. In such packages, the interposer 135 is customizedon the side facing the interconnects 140. For example, the interposer135 would be customized by the tracing of the interconnects 140 from thepre-defined pattern of the vias 150 to corresponding physical locationsof the pads 120 on the die 115.

[0052] However, it will be understood that the pattern of the solderballs 145 need not be pre-defined. Rather, the interposer 135 could havea pre-defined pattern for the physical location of the pads 120, and usethe interconnects 140 to trace to the vias 150 connected to a customizedpattern of the solder balls 145. Alternatively, the interconnects 140could connect customized patterns for both the pads 120 and the solderballs 145.

[0053] Furthermore, in one embodiment, the interposer 135 includesdeflection pockets 155. The deflection pockets 155 exist on theinterconnect-facing side of the interposer 135. Deflectable portions, orcantilevers 160, of the interconnects 140, extend above the deflectionpockets 155 such that when surface tension is applied to the tops of thecantilevers 160, it causes the cantilevers 160 to deflect downward intothe deflection pockets 155.

[0054] In one embodiment, the package 105 is mounted on the substrate110, where the substrate 110 comprises a printed circuit board. However,it will be understood that the substrate 110 could comprise a widevariety of materials for a wide variety of applications. For example, inone embodiment, the substrate 110 is a printed circuit board. One ofskill in the art, however, will recognize that the substrate can includea wide variety of materials including, but not limited to BT and FR4.

[0055] The substrate 110 includes conductive traces 165 electricallyconnected to substrate pads 170. The substrate pads 170 are configuredto correspond to, or match with, the physical location of the solderballs 145. The conductive traces 165 trace an electrical connection fromthe substrate pads 170 to any number of “off chip” systems or signals.

[0056] FIGS. 2-5 illustrate a package 200, according to anotherembodiment of the invention. In particular, FIGS. 2 and 4 illustrate aprocess of combining elements of the package 200 in order to deflect thecantilever 160 into a deflection pocket 155, while FIG. 3 illustrates atop view of the cantilever 160. FIG. 5 illustrates the package 200 afterreflow of the solder in the solder bump 125. It will be understood thatfor clarity, FIGS. 2-5 illustrate only one electrical connection madefrom the die 115, through the solder bump 125 and interconnect 140, tothe solder ball 145. As mentioned above, the die 115 may have manyelectrical connections through many solder bumps 125 and interconnects140, to many solder balls 145.

[0057]FIG. 2 illustrates a cross-sectional view of the package 200before attachment of the die 115. As shown in FIG. 2, the solder bump125 is attached to the die 115. In addition, the interposer 135, theinterconnect 160 and the adhesive 130 are configured to receive the.solder bump 125 and the die 115. As discussed above, the interposer 135comprises the via 150 and the deflection pocket 155. In FIG. 2, thesolder ball 145 has not yet been attached to the via 150. However, itwill be understood that the solder ball 145 could be attached andtherefore, the solder ball 145 is shown in broken lines in FIGS. 2, 4-6,and 8-9.

[0058] In one embodiment, the interconnect 140 is constructed bydepositing gold plated copper on to the interposer 135. Conventionaletching techniques are then used to create a desired pattern for theinterconnect 140. In certain embodiments, the interconnect 140 is tracedon the die-facing side of the interconnect 140. As discussed in furtherdetail below, the interconnect 140 can include a cantilever 160. Theskilled artisan will recognize that the interconnect 140 can be a widerange of conductors, conductive traces or the like. Furthermore, thecantilever 160 can in certain embodiments include deflectable portions,resilient portions, deformable portions, or malleable portions of theinterconnect 140.

[0059] The adhesive 130 attaches the interposer 135 and the interconnect140 to the die 115. In one embodiment, the adhesive 130 is selected suchthat it can withstand a temperature of at least about 150EC, forexample, Sumioxy LOC Tape, manufactured by Occidental ChemicalCorporation.

[0060] The adhesive layer 130 comprises at least one adhesive pocket133. In one embodiment, the adhesive pocket 133 extends through theadhesive layer 130 and partially into the interposer 135. In otherembodiments, the adhesive pockets 133 are holes that extend through theadhesive layer 130 and the interposer 135. The adhesive pocket 133 isdimensioned to receive the solder bump 125. In one embodiment, theadhesive pocket 133 is constructed by selectively applying adhesive tothe interconnect 140 and the interposer 135 using known techniques. Inother embodiments, the adhesive pocket 133 is constructed by screenprinting, drilling or punching the adhesive layer 130 or interposer 135.

[0061]FIG. 3 illustrates a top view of the interposer 135 and theinterconnect 140. In FIG. 3, the interposer 135 includes the deflectionpocket 155 surrounded by the interconnect 140. In one embodiment, thedeflection pocket 155 is approximately square in shape and does notextend entirely through the interposer 135. However, it will beunderstood that a wide variety of shapes could be used to form thedeflection pocket 155, for example, approximately circular, oval, orpolygonal shapes could be used. Furthermore, it will be understood thata wide variety of shapes of the interconnect 140 could be used tosurround the deflection pocket 155. For example, the shapes of theinterconnect 140 could either correspond to, or be different from, thewide variety of shapes of the deflection pocket 155. For example, thedeflection pocket 155 could be polygonal in shape and be surrounded bythe interconnect 140 in a circular fashion.

[0062] Also, the deflection pocket 155 could extend entirely through theinterposer 135 thereby creating another hole or via in the interposer135. While such a punched-through deflection pocket 155 is typicallyeasier to manufacture, it can expose the interior of the package 200 toenvironmental conditions after the die 115 and the solder ball 125 areattached.

[0063]FIG. 3 also illustrates the cantilever 160 extending over thedeflection pocket 155. In one embodiment, the cantilever 160 extendsapproximately half the distance across the deflection pocket 155.However, it is understood that one skilled in the art could manipulatethe flexibility and spring constant of the cantilever 160 by adjustingthe width and length thereof. The pattern of the interconnect 140 isshown deposited on a portion of the interposer 135 and over thedefection pocket 155. It will be understood by one of skill in the artthat the pattern of the interconnect 140 can be adapted for a variety ofpatterns and situations.

[0064]FIG. 4 illustrates a cross-sectional view of the package 200,after the die 115 and the solder bump 125 are affixed to the adhesive130. In one embodiment, the diameter of the solder bump 125 is largerthan the thickness of the adhesive 130, and therefore, the solder bump125 applies a surface tension to the cantilever 160. The surface tensiondeflects the cantilever 160 downward into the deflection pocket 155. Inone embodiment, the resilient deflected cantilever 160 applies apressure on the solder bump 125 that is directed towards the surface ofthe solder bump 125.

[0065]FIG. 5 illustrates a cross-sectional view of the package 200 afterreflow of the solder in the solder bump 125. When the solder in thesolder bump 125 reflows, it applies less surface tension to thecantilever 160, allowing the cantilever 160 to spring back in thedirection of the original position of the cantilever 160. As thecantilever 160 returns, it is at least partially absorbed by thereflowing solder. Thus, in one embodiment, the cantilever 160 applies aninwardly directed pressure to the solder bump 125 the urges thecantilever 160 into the solder bump 125.

[0066] It will be understood that the die 115, the solder bump 125, theadhesive 130, the interposer 135, the interconnect 140, and the solderball 145, could have a variety of sizes and thicknesses. As mentioned,the die 115 can be from a wide range of integrated circuit products. Forthis reason, the type of integrated circuit product will dictate thethickness of the die 115. In one embodiment, the die 115 is a dynamicmemory device with a thickness of approximately 280 microns. Also, inone embodiment, the thickness of the interconnect 140 and the cantilever160 is approximately 15 microns, the thickness of the interposer 135 isapproximately 48 microns, and the diameter of the solder ball 145 isapproximately 400 microns.

[0067] One advantage of the cantilever 160 is that the diameter of thesolder bump 125 and the thickness of the adhesive 130 can vary overwider ranges. For example, when the diameter of the solder bump 125 islarger than the thickness of the adhesive 130, the cantilever 160 isdeflected into the deflection pocket 155. Thus, in order to create anelectrical connection, the diameter of the solder bump 125 in thepackage 200 can be as thick or thicker than the adhesive 130. In oneembodiment, the diameter of the solder bump 125 is approximately 200microns and the thickness of the adhesive 130 is approximately 176microns.

[0068] The embodiment of FIGS. 2-5 thus provides the package 200 thathas electrical connections from the pads 120 on the die 115, through thesolder bumps 125 and the interconnects 140, to the solder balls 145. Thesolder bumps 125 deflect the cantilevers 160 when the die 115 is affixedto the adhesive 130. During reflow, the cantilevers 160 spring backtoward their original position and are thereby partially absorbed by thesolder bump 125. Deflection allows for relaxed tolerance requirementsbetween the diameter of the solder bump 125 and the thickness of theadhesive 130. Partial absorption allows for formation of an electricalconnection. These characteristics improve yield rates and therebydecrease the cost of package manufacture.

[0069] FIGS. 6-9 illustrate a package 600 according to yet anotherembodiment of the invention. In particular, FIGS. 6 and 8 illustrate aprocess of combining elements of the package 600 in order to deflectdual cantilevers 605 and 610 into a deflection pocket 615, while FIG. 7illustrates a top view of the dual cantilevers 605 and 610. FIG. 9illustrates the package 600 after reflow of the solder in the solderbump 125. It will be understood that for clarity, FIGS. 6-9 illustrateonly one electrical connection made from the die 115, through the solderbump 125 and interconnect 140, to the solder ball 145. As mentionedabove, the die 115 may have many electrical connections through manysolder bumps 125 and interconnects 140, to many solder balls 145.

[0070] Accordingly, FIG. 6 illustrates a cross-sectional view of thepackage 600 before attachment of the die 115. As shown in FIG. 6, thesolder bump 125 is attached to the die 115. Furthermore, the interposer135 includes the interconnect 140 traced on at least the die-facing sideof the interposer 135. In one embodiment, the interconnect 140 isdeposited on the interposer 135. Typical etching techniques are used tocreate a desired pattern for the interconnect 140.

[0071] The interposer 135 also includes the via 150 and the deflectionpocket 615. In one embodiment, the solder ball 145 has not yet beenattached to the via 150. The adhesive 130 is then added in order tocover both the interposer 135 and the interconnect 140. The adhesivepockets 133 are added, punched, drilled and screen printed. In certainembodiments, the pocket 615 and the via 150 comprise openings formed inthe interposer 135.

[0072]FIG. 7 illustrates a top view of the interposer 135 and theinterconnect 140. The interposer 135 includes the deflection pocket 615surrounded by the interconnect 140. In one embodiment, the deflectionpocket 615 is approximately square in shape and does not extend entirelythrough the interposer 135. However, it will be understood that a widevariety of shapes could be used to form the deflection pocket 615.Furthermore, it will be understood that a wide variety of shapes of theinterconnect 140 could be used to surround the deflection pocket 615.For example, the deflection pocket 615 could be polygonal in shape andbe surrounded by the interconnect 140 in a circular fashion.

[0073]FIG. 7 also illustrates the deflection pocket 615 as analternative to the deflection pocket 155 of FIGS. 2-5. The deflectionpocket 615 extends through the interposer 135. It will be understoodthat a skilled artisan would recognize that the deflection pocket 615could be used with the embodiment of FIGS. 2-5, and likewise, thedeflection pocket 155 could be adapted for use in FIG. 6.

[0074]FIG. 7 also illustrates the dual cantilevers 605 and 610 extendingover the deflection pocket 615 from opposite sides. Each of the dualcantilevers 605 and 610 is similar in composition and materialconsiderations as those mentioned in reference to the cantilever 160. Inone embodiment, each of the dual cantilevers 605 and 610 has a lengthwhich is approximately half the diameter or width of the deflectionpocket 615. In other embodiments, the first cantilever 605 may beapproximately a third of the width of the deflection pocket 615 whilethe second cantilever 610 may be approximately two-thirds the width ofthe deflection pocket 615. In yet other embodiments, the dualcantilevers 605 and 610 may each be less than approximately half thewidth of the deflection pocket 615.

[0075] It will be understood that a skilled artisan would recognize awide range of lengths and designs for the dual cantilevers 605 and 610.For example, directly opposite cantilevers may have a lower bound ontheir lengths being dictated only by the desire for some deflectiontherein. Moreover, the dual cantilevers 605 and 610 may be of differentlengths in order to exhibit different deflection distances. Thereby, thedual cantilever 605 and 610 would be absorbed into different areas ofthe solder bump 125.

[0076] Also, the dual cantilevers 605 and 610 could have lengths longerthan half the diameter, or half the width, of the deflection pocket 615by being offset from direct opposition of each other. In addition to theembodiments mentioned above, it is understood that a skilled artisan mayuse other designs for the dual cantilevers 605 and 610 directed to needsrecognizable to such an artisan. Also, it is understood that one skilledin the art could manipulate the flexibility and spring constant of eachof the dual cantilevers 605 and 610 by adjusting the widths and lengthsthereof.

[0077]FIG. 8 illustrates a cross-sectional view of the package 600,after the die 115 and the solder bump 125 are affixed to the adhesive130. In one embodiment, the diameter of the solder bump 125 is largerthan the thickness of the adhesive 130, and therefore, the solder bump125 applies a surface tension to the dual cantilevers 605 and 610. Thesurface tension deflects the dual cantilevers 605 and 610 downward intothe deflection pocket 615.

[0078]FIG. 9 illustrates a cross-sectional view of the package 600 afterreflow of the solder in the solder bump 125. When the solder in thesolder bump 125 reflows, it applies less surface tension to the dualcantilevers 605 and 610, allowing each of the dual cantilevers 605 and610 to spring back in the direction of their original position. As thedual cantilevers 605 and 610 return, they are at least partiallyabsorbed by the reflowing solder. Partial absorption creates anelectrical connection in spite of possible air pockets or bubbles.

[0079] Similar to FIGS. 2-5, use of the dual cantilevers 605 and 610 inthe package 600 allows the diameter of the solder bump 125 and thethickness of the adhesive 130 to have a more relaxed relationship. Forexample, when the diameter of the solder bump 125 is larger than thethickness of the adhesive 130, the dual cantilevers 605 and 610 aredeflected into the deflection pocket 615. Thus, in order to create anelectrical connection, the diameter of the solder bump 125 in thepackage 600 need only be as thick as the adhesive 130. On the otherhand, the diameter of the solder bump 125 may be as large as the maximumdeflection of the dual cantilevers 605 and 605. In one embodiment, thediameter of the solder bump 125 is approximately 200 microns and thethickness of the adhesive 130 is approximately 176 microns.

[0080] The embodiment of FIGS. 6-9 thus provides the package 600 thathas electrical connections from the pads 120 on the die 115, through thesolder bumps 125 and the interconnects 140, to the solder balls 145. Thesolder bumps 125 deflect the dual cantilevers 605 and 610 when the die115 is affixed to the adhesive 130. During reflow, the dual cantilevers605 and 610 spring back toward their approximate original position andare thereby partially absorbed by the solder bumps 125. Deflectionallows for relaxed tolerance requirements between the diameter of thesolder bumps 125 and the thickness of the adhesive 130. Partialabsorption allows for formation of an electrical connection. Thesecharacteristics improve yield rates and thereby decrease the cost ofpackage manufacture.

[0081]FIG. 10 illustrates a top view of yet another embodiment of theinvention. Similar to FIGS. 3 and 7, FIG. 10 includes the interposer 135having a deflection pocket 1010 (shown in broken lines) surrounded bythe interconnect 140. As with the deflection pocket 155, it will beunderstood that the deflection pocket 1010 could be many shapes and theinterconnect 140 may or may not correspond to such shapes. Furthermore,the deflection pocket 1010 could extend entirely through the interposer135. However, in one embodiment, the deflection pocket 1010 isapproximately square and extends only partially through the interposer135.

[0082] As further illustrated by FIG. 10, the interconnect 140 includesa series of flaps 1005 extending over and partially covering thedeflection pocket 1010. The flaps 1005 are made by depositing theinterconnect 140 over the deflection pocket 1010 and then etchingopenings 1015 therein. The deposition and etching are done by typicalmethods known to one of ordinary skill in the art of package design. Theopenings 1015 define the shape of the flaps 1005 and provide the abilityof the flaps 1005 to deflect downward into the deflection pocket 1010.It will be understood that the flaps 1005 could be a wide variety ofshapes and sizes. However, in one embodiment, the flaps 1005 comprisefour triangular-shaped flaps 1005, with each of the flaps 1005 havingone vertice in the approximate center of the deflection pocket 1010.

[0083] Although the foregoing invention has been described in terms ofcertain preferred embodiments, other embodiments will be apparent tothose of ordinary skill in the art. For example, a wide variety ofshapes and sizes of both the pockets and corresponding deflectableinterconnect portions may be combined to provide electrical connectionswithin a package. Additionally, other combinations, omissions,substitutions and modifications will be apparent to the skilled artisan,in view of the disclosure herein. Accordingly, the present invention isnot intended to be limited by the recitation of the preferredembodiments, but is instead to be defined by reference to the appendedclaims.

What is claimed is:
 1. A method of forming a ball grid array package foran integrated circuit by electrically connecting a plurality ofintegrated circuit pads to a plurality of solder balls, the methodcomprising: forming a plurality of conductive flaps over a pocket on afirst side of an insulating tape, wherein the pocket is configured to atleast partially accept a solder bump electrically connected to a pad ofan integrated circuit; forming a conductive trace terminating on secondside of the insulating tape at a solder ball, wherein the conductivetrace electrically connects the solder ball to the conductive flaps;attaching the integrated circuit to the insulating tape through anattachment layer having a thickness less than a diameter of the solderbump such that when attached, the solder bump deflects a deflectableportion of each conductive flap into the pocket, thereby creating acompliant connection between the integrated circuit and the conductiveflaps when the solder bump is activated; and activating the solder bumpto form a ball grid array package for the integrated circuit.
 2. Themethod of claim 1, wherein the attachment layer comprises an adhesivelayer.
 3. A method of forming a ball grid array package for anintegrated circuit, the method comprising: providing an integratedcircuit having pads each pad being electrically connected to one of anarray of solder bumps, providing an interposer including a plurality ofdeflectable conductive cantilevers positioned over a plurality ofopenings in the interposer, each deflectable conductive cantileverelectrically communicating with interconnect routed to ones of aplurality of solder ball connections; affixing an array of solder ballsto the plurality of solder ball connections; and forming a ball gridarray package for the integrated circuit by affixing the integratedcircuit to the interposer with an adhesive having a thickness less thanthe diameter of the one or more of the array of solder bumps, therebydeflecting the deflectable conductive cantilevers to form electricalconnections from the integrated circuit to array of the solder balls. 4.The method of claim 3, further comprising heating the array of solderbumps such that the deflected plurality of deflectable conductivecantilevers at least partially spring into the heated solder bumps. 5.The method of claim 3, wherein the plurality of deflectable conductivecantilevers positioned over a plurality of openings in the interposercomprise at least two conductive cantilevers over each opening.
 6. Themethod of claim 5, wherein the two conductive cantilevers oppose oneanother.
 7. The method of claim 5, wherein the two conductivecantilevers are different sizes.
 8. The method of claim 3, wherein theplurality of deflectable conductive cantilevers positioned over aplurality of openings in the interposer comprise deflectable flaps overeach opening.
 9. A method of enhancing an electrical connection betweenan integrated circuit and an array of solder balls in a ball grid arraypackage the method comprising: positioning an integrated circuitterminating in a plurality of solder connections having a thickness,over a plurality of interconnects extended over pockets in a tape,wherein the interconnects electrically connect to an array of solderballs on one side of the tape, wherein at least two interconnects extendover each pocket; combining the integrated circuit with the tape usingan adhesive having a thickness less that the thickness of the solderconnections such that the plurality of interconnects are deflected intothe pockets in the tape by the solder connections; and activating thesolder connections to allow the plurality of interconnects to springtowards their original position now inside the activated solderconnections, thereby forming an ball grid array package for theintegrated circuit.
 10. The method of claim 9, wherein the at least twointerconnects comprise flaps.
 11. The method of claim 9, wherein the atleast two interconnects are different sizes.
 12. A method for forming aball grid array (BGA) package for an integrated circuit, the methodcomprising: forming a first pocket in a first side of an interposer;forming a second pocket in a second side of the interposer; tracing aninterconnect in the interposer such that a plurality of conductive flapsextend over a portion of the first pocket forming a plurality ofcantilevers; affixing an integrated circuit to the first side of theinterposer using an adhesive having a thickness such that a solder bumpattached to the integrated circuit deflects the cantilevers into thefirst pocket; at least partially absorbing the cantilevers into thesolder bump; and affixing a solder ball at least partially within thesecond pocket, wherein the solder ball electrically connects to theinterconnect, thereby forming a BGA package for the integrated circuit.13. The method of claim 12, wherein the interposer comprises flexibletape.
 14. The method of claim 13, wherein the flexible tape comprisespolymide tape.
 15. The method of claim 13, wherein the flexible tapecomprises insulating material.
 16. The method of claim 13, wherein theflexible tape comprises at least one of thermoplastic, thermoplast,epoxy, flex circuit material, printed circuit board material, and fibermaterial.